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  <head>
    <meta charset="UTF-8">
    <title>Document</title>
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  <body>
    <script>
      console.log(typeof 12);			    	// 输出结果：number
      console.log(typeof '12');		    	// 输出结果：string
      console.log(typeof true);		    	// 输出结果：boolean
      console.log(typeof undefined);		// 输出结果：undefined
      console.log(typeof null);		    	// 输出结果：object
    </script>
  </body>
</html>